Precast, Prestressed Concrete for Bridge Decks : Technical Paper

A rapid method of replacing deteriorated bridge decks is desirable to minimize inconvenience and delays to the traveling public.A research project at Purdue University under the auspices of the Indiana State Highway Department and the Bureau of Public Roads has demonstrated the feasibility of using precast, prestressed concrete slabs for deck replacement.Plant manufacture of the slabs should result in a high quality, durable specimen.The pretensioned slabs (presently of U'-O" width) are placed transversely to the bridge girders.Pretensioning stress level is intended to maintain compression stress in the concrete under full design loads.The slabs are posttensioned in the longitudinal direction with cables strung through preformed slab ducts.A thin rubber pad placed in the joints between slabs minimizes stress concentrations due to surface irregularities.The pad and nominal post-tensioning stress level prevent water movement through the joint.Slab units are tied down to the supporting beams using spring clips and bolts screwed into preset anchors in the concrete.Laboratory research has dealt with the behavior of several joint shapes, with a flat key-type joint selected for field use.The number of tie-down bolts used provides adequate longitudinal slip resistance between the slab and the sup- porting beams.Static vertical load tests with load applied at a joint showed little shear transfer between loaded units and the adjacent unloaded slabs.An initial set of repeated load tests to simulate wheel passage over a joint showed distress at the joint, indicating the need for careful attention to joint detailing and forming.A second set of laboratory specimens, constructed with an improved joint detail withstood ten million cycles of repeated load application and showed no adverse effects.Two field installations are planned for the Spring of 1970, one as a re- placement deck for a heavily traveled bridge and the other on a newly installed bridge